Color of curves and their control elements, question 2
I don't know about the bezier curve thickness, but for the rest of the changes take a look below.

Go to user preferences (shortcut: Ctrl + Alt + U).Go to themes on the top and 3d view on the side.


Among these options,(10th row from top), 'vertex select' and 'vertex' will change the vertex colors for selected and non-selected vertices respectively.(both for bezier curves and mesh objects)



And in the 24th row, 'align handle selected' will change the handle colors of bezier curves in edit mode. Other settings for bezier curves, start with 'NURBS'



Scroll down until you see something like this.



'Vertex size' is for the size of bezier vertices and the usual mesh object vertices.